Mass mortality associated with koi herpesvirus in common carp in Iraq

Abstract

Koi herpesvirus disease is a serious disease affecting both wild and common carp species in different continents throughout the world. Based on pathological and molecular findings, we document the presence of koi herpesvirus disease in Iraq as a cause of mass mortality among the common carp of the Tigris river. On a macroscopic level, the fish exhibited variably sized skin ulcerations throughout the entire trunk. The gills showed variable degrees of discoloration with an increased amount of slimy mucus. Microscopically, degeneration and necrosis with infiltration of a heterogenous population of inflammatory cells characterized different organs, primarily the skin and gills, with occasional intranuclear inclusion bodies that are consistent with koi herpesvirus disease. A semi-nested PCR assay coupled with sequencing confirmed the pathological diagnosis. Genotyping and sequence analysis of the TK gene, ORF 136 and markers I and II identified the isolated CyHV-3 as variant A1 of the Asian genotype TUSMT1 (J strain) displaying the I⁺⁺II⁺ allele.

Keywords: Common carp; CyHV-3; Iraq; Mass mortalities; Microbiology; Virology.

Figure 1

Fish, carp, whole fish. Multiple variably sized and irregular skin ulcers (∗).

Figure 2

Fish, carp, gill. The gill exhibited variable degrees of discoloration and necrosis.

Figure 3

Fish, carp, kidney. Multifocally, the epithelial lining uriniferous tubules exhibited small, round and densely basophilic nuclei (pyknosis) with vacuolated cytoplasm (arrow). Eosinophilic-to-amphophilic intranuclear inclusion bodies were present in the haematopoietic cells (arrow head). H&E stain with 40× magnification.

Figure 4

Fish, carp, gill. A. Gill lamellae showed marked fusion of secondary lamellae, and hyperplasia of both epithelial cells covering lamellae and goblet cells with infiltration of mixed inflammatory cells. H&E stain with 4× magnification. Inset B is a higher magnification of A. H&E stain with 40× magnification.

Figure 5

Molecular phylogenetic analysis performed by the maximum likelihood method based on the Tamura 3-parameter model based on the partial nucleotide sequence of thymidine kinase genes of the Iraqi strain and other reference strains of CyHV-3. The scale bar represents a 5% change in nucleotides.